1. Field of the Invention
The present invention relates to an apparatus for supplying ink to an ink cylinder of a printer through an ink rail.
2. Description of the Related Art
An ink-furnishing method wherein ink is supplied to an ink cylinder of a printer through an ink rail has already been known as a particularly advantageous means which enables ink to be satisfactorily supplied even during a high-speed operation of a printer (see "General Printing Techniques" (revised edition), published by Sangyo Tosho, pp. 357 to 359, and "News Printing (the volume title: Printing)" (revised edition), published by Nihon Shinbun Kyokai, pp. 208 to 210).
The essential part of such ink rail is a concave surface having a curvature substantially equal to the radius of curvature of the peripheral surface of the associated ink cylinder. The ink rail is disposed in such a manner that this concave surface opposes the peripheral surface of the ink cylinder across a slight gap, e.g., 0.2 mm, so that about 1/4 of the entire periphery of the ink cylinder is constantly covered with the concave surface over the whole area in the axial direction. Accordingly, when an ink is delivered into the above-described gap from a tank by means of a pump through a row of discharge openings provided in the concave surface, the ink is attached to the peripheral surface of the ink cylinder and spread over the entire periphery of the cylinder as it is rotated.
A typical conventional ink rail is made of a cast iron material (JIS G5501 FC20), and the above-described concave surface for transferring ink is formed by smooth-finishing the surface of the cast iron material.
The kinds of ink which is transferred from such ink rail to the associated ink cylinder may be roughly classified into oleaginous ink and water-color ink on the basis of the media, i.e., vehicles, employed therefor.
The phenomenon that ink adheres to the surface of a solid substance is defined as "wetting" in terms of the interfacial chemistry, and the angle of contact between the surface of ink as a liquid and the surface of a solid substance is known as "contact angle". The smaller the contact angle, the smaller the surface tension of the liquid concerned, and the better the wetting of the solid surface; the larger the contact angle, the larger the surface tension of the liquid, and the worse the wetting of the solid surface (see "Printing Technology Handbook", edited by Nihon Insatsu Gakkai, published from Gihodo, pp. 121 to 145, and "Metallic Functional Surface", written by Yukio Murakawa, published from Kindai Henshu Sha, pp. 131 to 155).
As described above, the ink rail type ink-furnishing method has originally been developed for the purpose of increasing the operation speed of printers and of improving the printing effectiveness during the running of a printer over a long period of time.
However, when the operation speed of printers is increased to an ultra-high speed level in order to cope with the demand for mass printing in recent years, the conventional cast iron ink rail suffers from the following problem. Namely, the speed of transfer of ink from the cast iron surface to the peripheral surface of the ink cylinder cannot catch up with the speed of the printer, so that the supply of ink is interrupted, resulting in mottling of ink on the peripheral surface of the cylinder.
This phenomenon is particularly noticeable in offset presses using an oleaginous ink of high viscosity, but the occurrence of such phenomenon is also found in printing operations using a water-color ink of relatively low viscosity.